An organic EL (electroluminescence) light-emitting device is expected to be used in next-generation lighting as an alternative of a flat panel display, a fluorescent lamp, or the like.
In general, the organic EL light-emitting device is a stacked body of thin films, and the angle of total reflection of light between the thin films is determined by the difference in refractive index between the materials of the respective thin films. At present, approximately 80% of the light generated in the light-emitting layer is confined to the inside of the organic EL light-emitting device and it is not possible to extract the light to the outside. Specifically, the critical angle, θc, is 41.8° when the refractive index of a glass substrate is 1.5 and the refractive index of an air layer is 1.0, and the light with an angle of incidence smaller than this critical angle, θc, exits from the glass substrate to the air layer but the light with an angle of incidence greater than this critical angle, θc, is totally reflected to be confined to the inside of the glass substrate. Hence, it is desired to extract the light confined to the inside of the glass substrate on the surface of the organic EL light-emitting device to the outside of the glass substrate, namely, to improve the light extraction efficiency.
As a method for improving the light extraction efficiency of the organic EL light-emitting device, it is known to provide an optical film in which a plurality of microlenses are disposed on the light-exiting surface of the organic EL light-emitting device. As a method for producing such an optical film, a method in which an active energy ray-curable composition is directly dropped on a roll die, coated on the entire roll die, and cured is proposed in Patent Document 1 and Patent Document 2.